One important technique which has been developed to test the operation or functional status of semiconductor elements or the individual pins of integrated circuits is referred to as analog signature analysis. In the early development of this technique, the necessary electrical connections between the test instrument and the element/pin being tested were accomplished manually, such as by probes. An inspection of the resulting analog trace on the display of the test instrument was made by the operator, who determined the condition of the element based on his interpretation of the signature relative to a standard. The reliability of the test results thus depended to a significant extent on the skill and experience of the operator. This early development is exemplified by U.S. Pat. No. 3,973,198, issued on Aug. 3, 1976, in the name of Bill Hunt, and U.S. Pat. No. 4,074,195 issued on Feb. 14, 1978, also in the name of-Bill Hunt, both of which are owned by the assignee of the present invention.
In a further development of the analog signature analysis technique, a connection system was devised to automatically connect the test instrument sequentially to a plurality of test points, such as the successive pins in an integrated circuit, without any action required on the part of the operator. In addition in the further development, the analog signature signal obtained by the test instrument is converted into a set of digital signals which are representative of the analog value of the signature. These test digital signal values are then compared automatically with a previously stored reference set of digital values for the same element being tested. Operating under a selected protocol, any comparisons which yield a selected degree of differentness will be indicated to the operator.
The operator then can view those actual "different" analog signatures, following reconnection of the test instrument to the test points in question, to determine actual operating condition of the element. Alternatively, the element can be replaced on the basis of the results of the automatic comparison alone. Such an approach is exemplified by the structure shown in U.S. Pat. application Ser. No. 910,483 in the names of Yeung, et al., now U.S. Pat. No. 4,763,066 also owned by the assignee of the present invention, the contents of which are incorporated by reference herein.
However, even such further developments do not yield ideal results, since the automatic digital comparison is not completely accurate, and since the judgment of a trained operator is still important in many situations, necessitating that the element in question be connected again to the test instrument, in order that the analog signature be displayed In the present and still further development of analog signature analysis, full digitization, analog signature reconstruction, and particular display techniques and arrangements are used to further improve the operation and usefulness of the analog signature technique.